Remove special cases. Rely on DAG simplification

Signed-off-by: John Lu <John.Lu@amd.com>

Author: LU-JOHN

llvm/lib/Target/AMDGPU/AMDGPUISelLowering.cpp

@@ -4160,15 +4160,8 @@ SDValue AMDGPUTargetLowering::performSraCombine(SDNode *N,
     Hi = DAG.getFreeze(Hi);
     SDValue HiShift = DAG.getNode(ISD::SRA, SL, MVT::i32, Hi,
                                   DAG.getConstant(31, SL, MVT::i32));
-    SDValue LoShift;
-
-    if (RHSVal == 63)
-      LoShift = HiShift;
-    else if (RHSVal == 32)
-      LoShift = Hi;
-    else
-      LoShift = DAG.getNode(ISD::SRA, SL, MVT::i32, Hi,
-                            DAG.getConstant(RHSVal - 32, SL, MVT::i32));
+    SDValue LoShift = DAG.getNode(ISD::SRA, SL, MVT::i32, Hi,
+				  DAG.getConstant(RHSVal - 32, SL, MVT::i32));
 
     SDValue BuildVec = DAG.getBuildVector(MVT::v2i32, SL, {LoShift, HiShift});
     return DAG.getNode(ISD::BITCAST, SL, MVT::i64, BuildVec);